In modern media transmissions, many a time splicing of media streams is required, in which a transmitter that transmits one media stream splices into transmission of another media stream, wherein that transition is required to be as smooth and unnoticeable for a viewer/receiver as possible. By way of example, in television or digital radio broadcasting, advertisements may be inserted into a transmission of another program, wherein the transitions from the program to advertisement, between different advertisements, and back to the transmission of the program should desirably be as seamless as possible. This difficult task is even more difficult in system that implement multicasting and/or unicasting, such as system that implement targeted advertising in which different viewers/listeners receive different advertisement.
In prior art legal splicing between media stream, if stream B is being concatenated to stream A, the decoder must have all the required information to decode stream B upon transition—at the splice point. It is noted that the required information may pertain to different aspects of transmission if implemented, such as video related information, audio related information, and so forth.
For many audio-compression formats (e.g. MPEG audio, Dolby AC3, AAC-LC), any audio access unit (AU) can serve as a legal random access point and includes all required information to immediately start playing the encoded audio. However, the introduction of advanced audio tools e.g. SBR (Spectral Band Replication, ISO/IEC 14496-3:2003/Amd.1) and PS (Parametric Stereo, ISO/IEC 14496-3:2005/Amd.2) has changed this: Some decoding parameters are passed occasionally (in an optional header) and not for every AU. This introduces a new problem of splicing where not every AU is a random access point. Performing a legal splice in the audio domain for such audio formats requires handling a new problem.
Specifically, if the two streams have different decoding parameters (e.g. different advanced audio tools headers), specifying the new set of parameters must appear on the splicing point. Failure to do so will result in invalid decoding of the second audio stream until all parameters are correctly specified. Unfortunately, the second stream doesn't necessarily have these headers on the splice point. In fact the standards don't necessarily specify any requirement on the frequency of sending these headers.
Referring to the example of advertising offered above, it is noted that ads are expected to start with a random access point. Therefore, a splice between two ads should normally result in a legal audio stream since it is expected that upon the start of each ad, headers carrying all decoding parameters will appear prior to the data in order to allow decoding. In such a situation, a problem may still remain in generating a legal splice upon return to primary stream from an ad break. Since the there are no conditions on the repetition of optional headers in the primary, it is likely that there will be no header upon the return point and that the ad and primary decoding parameters will be different.
Another problem rises when splicing encrypted streams. There is no standard or common practice for specifying and synchronizing of audio random access points to transport layers. The existence and contents of optional audio headers are completely unknown when examining streams where the payload is encrypted.
Failure to solve these problems may result in syntax errors, audio high frequency noise and lip sync flaws. It is noted that output stream may become compliant again after appearance of headers specifying all the different parameters. However, the effect of syntax errors on the decoder is unknown.
There is therefore a need for technologies for enabling splicing between media streams wherein some of the media streams includes deciding parameters in only some of its access units.
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